Effect of different gases on the sonochemical Cr(VI) reduction in the presence of citric acid

DESTAILLATS, HUGO; CANCELADA, LUCÍA; MEICHTRY, JORGE M.; LITTER, MARTA I.

CHEMOSPHERE

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2020 vol. 260

0045-6535

The sonochemical (850 kHz) Cr(VI) reduction (0.30 mM, pH 2) in the presence of citric acid (Cit, 2 mM)was analyzed under different working atmospheres: reactor open to air without sparging (ROAWS), andAr, O2, air and N2 sparging. Hydrogen peroxide formation in pure water at pH 2 and KI dosimetry werealso measured. Zero-order kinetics was observed in all cases. A complete Cr(VI) reduction after 180 mininsonation was obtained with the ROAWS and under Ar, while a lower Cr(VI) reduction efficiency wasachieved under the other conditions. The Cr(VI) reduction and H2O2 formation rates followed the orderROAWS y Ar > air y O2[N2, while for KI dosimetry the order was ROAWS[O2 y air > Ar[N2.This indicates that H2O2 formation rate is a better measure of the system reactivity for Cr(VI) reduction.For air, O2 and N2, once the sparging was stopped, Cr(VI) reduction rate increased up to approximatelythe same value obtained for the ROAWS, suggesting that the sparging decreased the generation ofreactive species and, thus, the Cr(VI) reduction rate. Nitrate production was measured at low concentrations(micromolar range) in the ROAWS, air and N2 systems. Formic and acetic acids were detected asCit degradation products. Reaction mechanisms were proposed. It can be concluded that the best conditionfor Cr(VI) removal is with the ROAWS because of a higher Cr(VI) reduction rate, no atmospherecontrol is required, and it is a less expensive system.